Microstructure and creep behavior of an orthorhombic Ti-25Al-17Nb-1Mo alloy

Abstract

Microstructural evolution during three heat-treatment schedules and the terminal microstructures in an orthorhombic alloy of Ti-25Al-17Nb-1Mo were observed and analyzed with optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The creep behavior of the alloy with three different microstructures (a coarse-lath, fine-lath, and fine equiaxed microstructure) was studied over a temperature range of 600 ЊC to 750 ЊC and over a stress range of 150 to 400 MPa in air. The steady-state creep rates, apparent stress exponents, and apparent creep activation energies of the various samples have been determined. The results show that creep behaviors in the alloy are strongly influenced by microstructure. The effect on creep by some of the microstructural features, such as the multivariants within the coarse laths and the interfaces of the laths and the equiaxed grains, is also discussed.

The Microstructure, Creep, and Tensile Behavior for Ti-5Al-45Nb (Atomic Percent) Fully-β Alloy

“…Over the stress range of 34 to 75 MPa, the creep stress exponent transitioned to a value of 2.6, and a Q app value of 217 kJ/mol was measured at r = 75 MPa. The n values obtained within both stress regimes are in agreement with those previously reported for O + bcc Ti-Al-Nb alloys; [9][10][11][12][13][14]16,[24][25][26] however, the Q app values tended to be lower. The Q app values determined from creep experiments in the intermediate-stress and high-stress regime at 650°C for fully-O and O + bcc alloys fall in the range of 256 to 376 kJ/mol.…”

“…Several studies have focused on constructing microstructure-creep relationships and determining creep deformation mechanisms [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and constructing microstructure-tensile relationships of two-phase O + bcc Ti-Al-Nb alloys. [6,8,16,[18][19][20][21][22][23]25,[27][28][29][30][31][32][33] To some extent, the tensile and creep properties of fully-O microstructures and the tensile properties of fully-bcc microstructures have been characterized.…”

Oxidation and Diffusion in Ti-Al-(Mo, Nb) Intermetallics

“…[29][30][31][32] Alloys containing Nb less than 12 at. pct have a two-phase microstructure a 2 (hcp structure based on Ti 3 Al) and the high-temperature phase b/B2 (bcc structure).…”

Abnormal acceleration of creep deformation rate above 700°C in the orthorhombic based Ti–22Al–27Nb alloy

“…The Ti 2 AlNb-based alloys with a two-phase microstructure (orthorhombic-bcc) are known to have better mechanical properties than those of conventional alpha-2 based alloys [3]. Since the microstructure of Ti 2 AlNb alloy can be easily controlled with various heat-treatment schedules [4][5][6][7][8], the relationship between microstructure/mechanical properties have been frequently reported in the last decade [9][10][11][12]. In these reports, attention has been focused on the modified microstructures and heat-treatment processes to achieve a good balance of mechanical properties.…”

“…In these reports, attention has been focused on the modified microstructures and heat-treatment processes to achieve a good balance of mechanical properties. The transient creep behavior of primary strain [11,13] and the calculation of apparent creep activation energy of different Ti 2 AlNb-based alloys [10,[12][13][14][15] have been investigated. It has been reported that the tensile strength of O + bcc dual phase alloys is significantly decreased above 700 • C regardless of aging condition and alloy composition.…”